上游充通大学 SHANGHAI JIAO TONG UNIVERSITY Engineering Thermodynamics I Lecture 9-10 Spring,3/11/2019 Prof.,Dr.Yonghua HUANG 强 MAMLLLAMAAA http://cc.sjtu.edu.cn/G2S/site/thermo.html 1日G
Engineering Thermodynamics I Lecture 9-10 Spring, 3/11/2019 Prof., Dr. Yonghua HUANG http://cc.sjtu.edu.cn/G2S/site/thermo.html
Pure Substance A substance is uniform and fixed in chemical composition i.e.water,N2,He,CO2,etc. A mixture of chemical elements or compounds is treated as a pure substance as long as mixture is homogeneous i.e.gaseous Air (pseudo-pure substance) A mixture of two or more phases could still be a pure substance as long as chemical composition of each phase is same i.e.ice and liquid water Vapor Air but not liquid and gaseous air Liquid Liquid (a)H20 (b)Air 上游通大学 March 12,2019 2 SHANGHAI JLAO TONG UNIVERSITY
March 12, 2019 2 Pure Substance A substance is uniform and fixed in chemical composition i.e. water, N2 , He, CO2 , etc. A mixture of chemical elements or compounds is treated as a pure substance as long as mixture is homogeneous • i.e. gaseous Air (pseudo-pure substance) A mixture of two or more phases could still be a pure substance as long as chemical composition of each phase is same • i.e. ice and liquid water • but not liquid and gaseous air
Fixing the state state of a closed system at equilibrium is described by the values of its intensive thermodynamic properties not all independent Question:how many independent properties are need to fix the state? state principle:number of independent properties =1+number of relevant work interactions Energy altered independently by >W=Jpdv,boundary volumetric work only Simple compressible system Quasi-equilibrium 上游充通大 March 12,2019 3 SHANGHAI JIAO TONG UNIVERSITY
March 12, 2019 3 Fixing the state Simple compressible system Quasi-equilibrium W= ∫pdV, boundary volumetric work only Q Energy altered independently by state principle : number of independent properties = 1+ number of relevant work interactions state of a closed system at equilibrium is described by the values of its intensive thermodynamic properties not all independent Question: how many independent properties are need to fix the state?
State principle for simple compressible system Gas →p=TW,i,W.… +V- Gas →fTp),u=fT,p),… Gas -→T=fv,p,u=fy,p),… Intensive properties such as velocity and elevation that are assigned values relative to datums outside the system are excluded from present considerations. 上游充通大 March 12,2019 4 SHANGHAI JLAO TONG UNIVERSITY
March 12, 2019 4 State principle for simple compressible system Gas T +v p=f(T,v), i=f(T, v), … Gas T +p v=f(T,p), u=f(T, p), … Gas v +p T=f(v,p), u=f(v, p), … Intensive properties such as velocity and elevation that are assigned values relative to datums outside the system are excluded from present considerations
Phases of a Pure Substance Phase refers to a quantity of matter that is homogeneous throughout in both chemical composition and physical structure (a) (b) (c) (a)Solid:molecules oscillate about "fixed"positions (b)Liquid:groups of molecules float about each other (c)Gas:gas molecules move randomly 上游究通大学 March 12,2019 5 SHANGHAI JLAO TONG UNIVERSITY
March 12, 2019 5 Phases of a Pure Substance (a) Solid: molecules oscillate about “fixed” positions (b)Liquid: groups of molecules float about each other (c)Gas: gas molecules move randomly Phase refers to a quantity of matter that is homogeneous throughout in both chemical composition and physical structure